The Stormers were last in action against the Sharks a fortnight ago when substitute Grant rescued them with a last-gasp penalty for a 15-12 win.
Van Aswegen has been relegated to the reserves' bench, which is the only change to their starting line-up.
"Grant is a Springbok, and an experienced player," said Coetzee.
"We had a look at the opposition, and we agreed that they are a tough outfit, with loads of experience in their ranks. Grant also has experience and he can cope with pressure, which the Blues are sure to exert."
The Stormers mentor would have been tempted to call-up the ever-improving lock Rynhardt Elstadt and prop Deon Carstens after injury lay-offs but he decided to give them game time with the Western Province side in their Vodacom Cup match against the Sharks XV in Durban, on Saturday.
"Elstadt and Carstens will do well to enjoy some game time at Vodacom Cup level and that will also help to prime them for our tour matches in a few weeks' time," he said.
Despite his Newlands heroics a fortnight ago, Grant is not the side's automatic choice as goalkicker.
"Since the start of the season Joe Pietersen has done the job for us but as is the case with every match, we make a decision at the captain's run, a day before the match," said Coetzee.
"We take into account how the place-kickers perform at the pre-match sessions."
Despite the fact that the New Zealand visitors will be playing without their World Cup-winning flanker Jerome Kaino (injured) and stand-out backliner Rene Ranger (suspended), Coetzee felt that the Blues' victory over the Bulls in Pretoria last weekend would fuel their confidence substantially.
"This Blues side force their opponents into making mistakes and we saw how they did that at Loftus last week," said Coetzee.
"It has never been easy to win at Loftus, but this team did just that.
"This team has from the outset been tough and decisive.
"Earlier in the season they could have beaten the Crusaders too."
Teams:Stormers:
15 Joe Pietersen, 14 Gio Aplon, 13 Juan de Jongh, 12 Jean de Villiers (captain), 11 Bryan Habana, 10 Peter Grant, 9 Dewaldt Duvenage, 8 Nick Koster, 7 Duane Vermeulen, 6 Siya Kolisi, 5 Andries Bekker, 4 Eben Etzebeth, 3 Brok Harris, 2 Tiaan Liebenberg, 1 Steven Kitshoff
Substitutes: 16 Scarra Ntubeni, 17 Frans Malherbe, 18 De Kock Steenkamp, 19 Nizaam Carr, 20 Louis Schreuder, 21 Gary van Aswegen, 22 Gerhard van den Heever
Blues:
TBA
Referee: Glen Jackson (NZ)